The invention generally relates generally to a method of fabricating a photomask, and more particularly, to a method of fabricating a photomask using a Self Assembly Molecule (SAM).
Generally, a semiconductor device is formed of numerous patterns. These patterns are made by a photolithography process that includes exposure, development, and etch processes, using a photoresist layer pattern as an etch mask. More specifically, the exposure process is one in which the pattern on a photomask is transferred to a photoresist layer on a wafer. Therefore, when the pattern on the photomask is not accurately formed, it is impossible to obtain the desired photoresist layer pattern.
Recently, as degree of semiconductor device integration has increased, the size of the pattern has decreased and and become finer. Presently, an electron beam lithography method or a laser beam method are typically used as a method of forming patterns on the photomask. In a phase shift mask, for example, a phase shift layer, a chrome layer, and a resist layer are sequentially formed on a transparent substrate. Next, a resist layer pattern is formed by performing exposure and development by an electron beam lithography or a laser beam lithography on the resist layer. A phase shift layer pattern and a chrome layer pattern that expose a light transmitting region of the transparent substrate are formed by sequentially removing the exposed portions of the chrome layer and the phase shift layer, using the resist layer pattern as an etch mask. Then, the resist layer pattern is removed, and the chrome layer pattern in the rest portion except for a frame region is subsequently removed.
Although exposure by the electron lithography method or a laser beam lithography method makes it easy to form fine patterns, compared to an exposure by a photolithography method, there are various problems in forming ultra fine patterns due to the rapid increase in the integration degree of semiconductor devices. For example, the lithography apparatus, the exposure apparatus, development apparatus, and the etching apparatus should be continuously improved to obtain and ensure more fine patterns. Also, development of a resist layer material required in the electron beam lithography process or a laser beam lithography process should be performed together. However, now, the improvement of the apparatus and development of the material cannot keep up with required increase in the integration degree.